Efficient dword bitwise rotate / circular shift using Bash shell ?

[SugarBug]

Example:

rol() { num="$@" ; pre=$((num<<13)) ; suf=$((num>>19)) ;
num=$((pre^suf)) ; num=$((num&0xffffffff)) ; echo "$num" ; }

What tricks will make this more efficient in Bash?

[Phil Carmody]

Post by SugarBug
num=$((pre^suf)) ; num=$((num&0xffffffff)) ; echo "$num" ; }
What tricks will make this more efficient in Bash?

If you can be sure the input will never be 0xffffffff, then this should
work:

rol () { echo "$(($1*8192%0xffffffff))" ; }

Phil

[Jakob Bohm]

Post by Phil Carmody

Post by SugarBug
num=$((pre^suf)) ; num=$((num&0xffffffff)) ; echo "$num" ; }
What tricks will make this more efficient in Bash?

If you can be sure the input will never be 0xffffffff, then this should
rol () { echo "$(($1*8192%0xffffffff))" ; }
Phil

rol13() { printf '0x%X' $(((($1<<13)+($1>>19))&0xffffffff))
}

Avoids that limitation, but may be slightly slower depending on bash
inefficiencies.


Enjoy

Jakob